ROME -- Less than a month after a court in Sicily sentenced 19 Mafia bosses to life imprisonment, Italy's judiciary has shifted its attention to a group of prominent Sicilian politicians and businessmen suspected of having supported and helped the crime syndicate.

Palermo's assistant prosecutor, Paolo Giudici, ordered indictments last week against four former mayors, three former city councilmen and a group of prominent local contractors. They are all accused of crimes connected with public works contracts signed between Mafia-backed companies and the city government.

The judicial action came within days of the murder of former mayor Giuseppe Insalaco, who, for the past three years, has been testifying in secret to investigators about the links between the Mafia and his city's traditional political and business leadership.

Insalaco, 46, had been mayor of Palermo for only four months in 1984 before quitting with a denunciation of corruption in City Hall. On Tuesday, he was gunned down by two men on a motorscooter. His death was followed two days later by another apparent Mafia murder -- of Natale Mondo, 36, a policeman, who was a one-time confidant of an anti-Mafia police commissioner assassinated in 1985. It could not be immediately established if there was a link between Insalaco's and Mondo's murders.

Their deaths were the fourth and fifth since the end of the trial last month that represented the Italian state's most determined effort to crush the power of the crime underground in Sicily. That network reportedly controls a major part of the heroin trade to the United States and dominates the illegal -- and, according to state investigators, much of the legal -- contracting and development business in Sicily.

"What we are seeing is the Mafia's reaction to the moves to curtail its power in Sicily as represented by the new reformist political leadership that has come to power in recent years," said Pino Arlacchi, a prominent sociologist who has specialized in studying the Mafia.

In a telephone interview, Arlacchi said last month's trial of 452 accused Mafia members struck at "the military side of the organization, while the reformist political leadership that today runs Palermo is a blow to its political power."

Arlacchi, who was a member of the State's Anti-Mafia Commission that expired last year, has long argued that one of the most insidious aspects of Mafia power in Italy is the "political Mafia lobby" that supports it.

It is that lobby, made up mostly of members of the Christian Democratic Party that dominates Sicilian -- and Italian -- politics, that is now targeted by the Italian judiciary for its links to the mob.

All four of the indicted former mayors -- Vito Ciancimino, Giacomo Marchello, Carmelo Scoma and Nello Martellucci -- and two of the three charged former city councilmen were members of the Christian Democratic Party. Until the rise of reformist Mayor Leoluca Orlando in 1985, the party in Sicily had long been believed linked to the Mafia.

Judicial authorities said the former politicians were believed to have supported the Mafia's efforts to control public works contracts with the state while they were in office.

"Though everyone thinks the Mafia's major income is drugs, the fact is that construction and public works from the state are one of their most lucrative sources of finance," said one judicial source.

Judicial authorities here speculated that Insalaco was killed as a warning to others not to corroborate his testimony.